Optical receivers are used in optical transponders or transceivers, to enable communications equipment to operate over fiber optic lines. A typical problem is that high data rate optical signals can be significantly impaired by a characteristic of the optical fiber referred to as “fiber chromatic dispersion”. High data rate in this case refers to 5 gigabits per second (Gpbs) and higher. Data that is transmitted over optical fiber is typically formatted into symbols, in accordance with a popular protocol referred to as NRZ OOK “non-return to zero on/off keying”, a binary form of intensity modulation. NRZ OOK coding is an example of the more general binary coding format, where data is translated into a stream of symbols where each symbol can have one of only two values, and accordingly the transmission line signal has one of only two stable states.
More recently, another signaling format has been developed referred to as “duo-binary” which occupies less bandwidth than a binary format, for the same data rate. Duo-binary data formats are less susceptible to single mode fiber chromatic dispersion, as well as other link distortions. However, generating duo-binary signals on the transmit end of a fiber link typically requires the use of costly and relatively uncommon optical and electrical components.